sysdeps/ieee754/dbl-64/s_logb.c

   1 /* @(#)s_logb.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 /*
  14  * double logb(x)
  15  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  16  * Use ilogb instead.
  17  */
  18
  19 #include <math.h>
  20 #include <math_private.h>
  21
  22 double
  23 __logb (double x)
  24 {
  25   int32_t lx, ix, rix;
  26
  27   EXTRACT_WORDS (ix, lx, x);
  28   ix &= 0x7fffffff;             /* high |x| */
  29   if ((ix | lx) == 0)
  30     return -1.0 / fabs (x);
  31   if (ix >= 0x7ff00000)
  32     return x * x;
  33   if (__builtin_expect ((rix = ix >> 20) == 0, 0))
  34     {
  35       /* POSIX specifies that denormal number is treated as
  36          though it were normalized.  */
  37       int m1 = (ix == 0) ? 0 : __builtin_clz (ix);
  38       int m2 = (lx == 0) ? 0 : __builtin_clz (lx);
  39       int ma = (m1 == 0) ? m2 + 32 : m1;
  40       return -1022.0 + (double)(11 - ma);
  41     }
  42   return (double) (rix - 1023);
  43 }
  44 weak_alias (__logb, logb)
  45 #ifdef NO_LONG_DOUBLE
  46 strong_alias (__logb, __logbl) weak_alias (__logb, logbl)
  47 #endif